1. Field of the Invention
The present invention relates to a display unit for inputting a video signal and displaying an image corresponding to the video signal and more particularly to an image display unit suitable for displaying an image having aspect ratio different from the aspect ratio of the effective screen of a display on which an image is displayed.
2. Description of the Related Art
A conventional type display unit for inputting a video signal such as a television signal and displaying it on a display such as a cathode-ray tube (CRT) and a liquid crystal panel is provided with various means to prevent a displayed image from being distorted in case the aspect ratio of the effective screen of the display and the aspect ratio of an input video signal are different.
For example, a case that a video signal having the aspect ratio of 3:4 is displayed on a display unit provided with an effective screen having the aspect ratio of 9:16 will be described below. FIG. 1 shows an original image input as a video signal and having the aspect ratio of 3:4. This original image is composed of a large circle in the center and four small circles touched to the circumference of the large circle.
FIGS. 2A to 2C show an example that the original image shown in FIG. 1 and having the aspect ratio of 3:4 is displayed on a display unit provided with an effective screen having the aspect ratio of conventional 9:16. FIG. 2A shows a state in which the original image is displayed as it is in the lateral direction and the ratio of 3:4 of a video signal is kept in the longitudinal direction so that the image is not distorted. In this case, the image is cut off by approximately 25% in the upper and lower parts. FIG. 2B shows a state in which the original image is displayed as it is in the longitudinal direction and the original image is extended in the lateral direction so that it is matched with the ratio of the effective screen. In this case, the image is distorted and looks to be pressed longitudinally, that is, extended laterally as a whole. FIG. 2C shows a state in which the original image is displayed as it is in the longitudinal direction and the ratio of 3:4 of an original image is kept so that the image in the lateral direction is not distorted. In this case, the right and left sides of the screen are largely vacant and the screen of the display cannot be effectively used.
As shown in FIG. 2C, to display an original image in the image display device having an effective screen whose aspect ratio is 9:16 in a state that an aspect ratio of 3:4 is maintained, the amplitude of horizontally deflecting current must be reduced. In this case, as described below, however, there is a problem that image information at right and left corners cannot be displayed correctly due to ringing of horizontally deflecting current.
In other words, immediately after the start of tracing, randomness of waveforms occurs in horizontally deflecting current due to ringing components caused by the inductance of a horizontally deflecting coil and resonance of interline capacity, etc., scanning speed of electric beam is delayed, and thus the image at the right and left corners is deformed. As shown in FIG. 2C, to display an original image in the image display device having an effective screen whose aspect ratio is 9:16 in a state that an aspect ratio of 3:4 is maintained, the video signals corresponding to the image portions at the right and left corners of the screen must therefore be blanked so that deformed portions of the image cannot be seen. The image information at the right and left corners is cut off, and so the whole image information at the horizontal period cannot be displayed.
To solve the above problems, there is also a display unit provided with an image mode for displaying the whole image or almost all parts by distorting only a part of the image. FIGS. 3A and 3B show other examples in which the image shown in FIG. 1 is displayed on such a conventional type display unit. In such a conventional type display unit, an image is prevented from being distorted by approximating the roundness in the vicinity of the center in which the most important information on the screen is displayed to one and the image is gradually extended laterally as both ends approach. FIG. 3A shows a state in which the image is displayed as it is in the longitudinal direction on such a display unit. FIG. 3B shows a state in which the image is displayed with a scan rate in the longitudinal direction increased to prevent both ends from being extended laterally in such a display unit. In any case, the aspect ratio of the image is inaccurate in almost all parts of the screen.
As described above, in the conventional type display unit, to display an image without distortion, the image has to be displayed on the screen different in aspect ratio with the aspect ratio of the image kept and there is a problem that an important part of an image may be cut off or only a part of an effective screen is used. If an image is all displayed with it matched with a screen the aspect ratio in a part or the whole of an image has to be changed and there is a problem that the whole or a part of the image is distorted. As the size of an image and slight distortion on right and left sides also change if the linearity of a raster is changed as described above, there is a problem that readjustment of a raster is required.
The present invention is made to solve such problems and the object is to provide a display unit wherein the effective screen can be utilized up to the maximum without distorting a displayed image.
In the present invention, to solve the above problems, a display unit characterized in that signal processing means for generating a compressed video signal acquired by compressing the whole image information in a horizontal cycle of an input signal on time base, synchronizing signal generating means for generating a synchronizing signal for fixing phasic relationship with the above compressed video signal based upon a synchronizing signal separated from the input signal and display means for displaying the above compressed video signal together with the above synchronizing signal are provided to the display unit for displaying an input video signal is provided.
In the display unit composed as described above, the signal processing means compresses the whole image information in a horizontal cycle of an input video signal on a time basis and generates a new compressed video signal corresponding to a display and the synchronizing signal generating means generates a synchronizing signal corresponding to the new compressed video signal generated by the signal processing means based upon a synchronizing signal separated from the input signal. The display means controls scanning by an electron beam according to the new synchronizing signal generated by the synchronizing signal generating means and displays the generated new compressed video signal on the display.